Ann: Trading Halt, page-27

"why they can’t send a mini tunnel borer with sensors into one of those subterranean streams of gold and track the seam that way rather than scissoring in from ground level."

Is a machine like that available for exploration in hard rock given most TBMs are used in soft rock in mining ?
Also a TBM would create powder and not a core as in Diamond drilling (DD) powder is ok to determine tenor (grade of ore as in RC drilling )but it does not show the structure ie the bands you see in DD core which shows orientation of the ore body
Also It would need to be of relatively small diameter guessing less than 100mm both because of the extra energy and wear and tear on machinery and because of the high pull back needed on the drill frame to lift the TBM ie 400 meters of drill string is very heavy when a wide bore Ie HQ rod size
The scissoring tends to be used only occasionally think normally by diamond drilling (which has core) to determine initial structure of the seam normally they drill the next hole along where they think the ore body is striking and try to keep the drill hole as close as possible perpendicular to the orientation of the seam from vertical (its dip) to get a truish intercept width unless it is a flat lying ore body (tabular ) in which case they just drill vertically down to get true width of the ore body .
They do drop sensors down drill holes to do Electro magnetic analysis

I am not a miner so just my relatively uneducated opinion .